The present invention relates to solid state semi-conductor switching devices having at least two electrodes, the impedance between the two electrodes being relatively very low in one state and very high in the other state.
Solid state switches are known in which a p-n junction is positioned in close proximity to a two-layer system comprising an electrode and a thin layer of silicon dioxide. A further electrode is positioned remote from the other electrode on the other side of the p-n junction. It is the interaction between the junction and the two-layer system which gives the device its switching property. In an alternative known switching device the silicon dioxide is replaced by a semi-insulating layer usually of polycrystalline silicon.
Solid state switches of the types mentioned suffer from two disadvantages: firstly since the interfaces between the electrode and silicon dioxide or polycrystalline material depend on the condition of the surface on which the electrode is deposited, such interfaces have notoriously variable properties from one device to another and suffer large characteristic variation with temperature; and secondly the characteristics of the electrode/oxide or electrode/polycrystal are fixed within a small range for any two interface materials and thus the interface is not amenable to "design" of characteristics.